1. Field of the Invention
This invention relates to a process for producing a polyarylene sulfide and, more particularly, to a process for producing a polyarylene sulfide having a high molecular weight, a high purity, excellent color tone and excellent heat stability.
Polyarylene sulfide (for example, a polyphenylene sulfide), having excellent heat resistance and excellent chemical resistance, has attracted special attention for use in electronic components and automotive parts. Being moldable into various formed parts, films, sheets, fibers, etc. by injection, extrusion or other molding process, polyarylene sulfide is widely used in fields where heat resistance is needed.
2.Description of the Prior Art
Japanese Patent Publication No. 3368/1970 discloses a process for producing a polyarylene sulfide wherein the reaction between a dihalogenated aromatic compound and a sulfur source such as sodium sulfide or the like is conducted in an organic amide solvent such as N-methyl-2-pyrrolidone.
However, the molecular weight of the polymer obtained by this process is not sufficiently high to be used for injection molding or the like. Therefore, this low-molecular weight polymer is heated in the air so as to be crosslinked through oxidation, thereby enabling the polymer to be used for molding process. However, even such a polymer having an increased molecular weight suffers from inferior extrudability which may be attributed to the high level of crosslinking and branching, so that it has heretofore been difficult to form said polymer into films or fibers.
Under these circumstances, processes for obtaining a high-molecular weight polyarylene sulfide through polymerization reaction have been proposed. A typical example of this type of prior art is a process disclosed in Japanese Patent Publication No. 12240/1977 in which polymerization reaction is conducted in the presence of R-COOM (R is a hydrocarbyl group and M is an alkali metal) which is employed as a polymerization auxiliary. The high-molecular weight polymer obtained in this way is considered to be excellent in terms of extrudability and hence applicable to formation of films, fibers, etc.
The above-described process, however, causes the corrosion of reaction vessels, resulting in elution of heavy metals into the resulting polymer. Therefore, a significant amount of heavy metals remains in the polymer produced by said reaction, which unfavorably causes a reduction in color tone and heat stability and the like.